Use template context function for avatar rendering (#26385)

Introduce `AvatarUtils`, no need to pass `$.Context` to every
sub-template, and simplify the template helper functions.

templates/repo/settings/lfs_locks.tmpl

@@ -31,7 +31,7 @@
 							</td>
 							<td>
 								<a href="{{$.Owner.HomeLink}}">
-									{{avatar $.Context $.Owner}}
+									{{ctx.AvatarUtils.Avatar $.Owner}}
 									{{$.Owner.DisplayName}}
 								</a>
 							</td>